affordable learning management systems

Our university is leading a four-week program design academy this spring for local nonprofits. I am trying to identify a learning management system (LMS) that can hold the readings and give participants a chance to upload "assignments" for review. Also having the ability to answer discussion forums would be an added bonus. Since participants are not actual students our university system will not work. Does anyone have suggestions for a LMS or other platform that they have used in the past that might meet our basic needs beyond a makeshift Dropbox or Facebook Group?

Here are three of the suggestions that were offered:

Canvas is a robust but fairly easy LMS to learn and use. I believe there is a free though limited version for teachers and students that might meet your needs.

When I was leading a study abroad course last summer in Argentina, without access to my university's LMS (Canvas), I found Google Classroom worked fairly well to organize assignments, and keep students updated on what I was working on. Students can also upload assignments, and you can provide readings there as well. You can also grade in it, but I didn't use that function. You can create blog post type assignments in google classroom that allow for online posts and replies. It's not robust, but it's free. Classroom.google.com.

I believe you can set up a media wiki for free and that they are less data consuming (stealing) than google products. I used to use Wikispaces with very good results, but they closed last year.